I recently got fairly confused why the following expression didn't have
any effect
{
description = "Foobar";
inputs.sops-nix = {
url = github:mic92/sops-nix;
inputs.nixpkgs_22_05.follows = "nixpkgs";
};
}
until I found out that the input was called `nixpkgs-22_05` (please note
the dash vs. underscore).
IMHO it's not a good idea to not throw an error in that case and
probably leave end-users rather confused, so I implemented a small check
for that which basically checks whether `follows`-declaration from
overrides actually have corresponding inputs in the transitive flake.
In fact this was done by accident already in our own test-suite where
the removal of a `follows` was apparently forgotten[1].
Since the key of the `std::map` that holds the `overrides` is a vector
and we have to find the last element of each vector (i.e. the override)
this has to be done with a for loop in O(n) complexity with `n` being
the total amount of overrides (which shouldn't be that large though).
Please note that this doesn't work with nested expressions, i.e.
inputs.fenix.inputs.nixpkgs.follows = "...";
which is a known problem[2].
For the expression demonstrated above, an error like this will be
thrown:
error: sops-nix has a `follows'-declaration for a non-existant input nixpkgs_22_05!
[1] 2664a216e5
[2] https://github.com/NixOS/nix/issues/5790
Overrides for inputs with flake=false were non-sticky, since they
changed the `original` in `flake.lock`. This fixes it, by using the same
locked original for both flake and non-flake inputs.
this slightly increases the amount of memory used for any given symbol, but this
increase is more than made up for if the symbol is referenced more than once in
the EvalState that holds it. on average every symbol should be referenced at
least twice (once to introduce a binding, once to use it), so we expect no
increase in memory on average.
symbol tables are limited to 2³² entries like position tables, and similar
arguments apply to why overflow is not likely: 2³² symbols would require as many
string instances (at 24 bytes each) and map entries (at 24 bytes or more each,
assuming that the map holds on average at most one item per bucket as the docs
say). a full symbol table would require at least 192GB of memory just for
symbols, which is well out of reach. (an ofborg eval of nixpks today creates
less than a million symbols!)
Pos objects are somewhat wasteful as they duplicate the origin file name and
input type for each object. on files that produce more than one Pos when parsed
this a sizeable waste of memory (one pointer per Pos). the same goes for
ptr<Pos> on 64 bit machines: parsing enough source to require 8 bytes to locate
a position would need at least 8GB of input and 64GB of expression memory. it's
not likely that we'll hit that any time soon, so we can use a uint32_t index to
locate positions instead.
Starting work on #5638
The exact boundary between `FetchSettings` and `EvalSettings` is not
clear to me, but that's fine. First lets clean out `libstore`, and then
worry about what, if anything, should be the separation between those
two.
we'll retain the old coerceToString interface that returns a string, but callers
that don't need the returned value to outlive the Value it came from can save
copies by using the new interface instead. for values that weren't stringy we'll
pass a new buffer argument that'll be used for storage and shouldn't be
inspected.
When we check for disappeared overrides, we can get "false positives"
for follows and overrides which are defined in the dependencies of the
flake we are locking, since they are not parsed by
parseFlakeInputs. However, at that point we already know that the
overrides couldn't have possible been changed if the input itself
hasn't changed (since we check that oldLock->originalRef == *input.ref
for the input's parent). So, to prevent this, only perform this check
when it was possible that the flake changed (e.g. the flake we're
locking, or a new input, or the input has changed and mustRefetch ==
true).
Previously, when we were attempting to reuse the old lockfile
information in the computeLocks function, we have passed the parent of
the current input to the next computeLocks call. This was incorrect,
since the follows are resolved relative to the parent. This caused
issues when we tried to reuse oldLock but couldn't for some
reason (read: mustRefetch is true), in that case the follows were
resolved incorrectly.
Fix this by passing the correct parent, and adding some tests to
prevent this particular regression from happening again.
Closes https://github.com/NixOS/nix/issues/5697
When an input follows disappears, we can't just reuse the old lock
file entries since we may be missing some required ones. Refetch the
input when this happens.
Closes https://github.com/NixOS/nix/issues/5289
When setting flake-local options (with the `nixConfig` field), forward
these options to the daemon in case we’re using one.
This is necessary in particular for options like `binary-caches` or
`post-build-hook` to make sense.
Fix <343239fc8a (r44356843)>
Rather than having them plain strings scattered through the whole
codebase, create an enum containing all the known experimental features.
This means that
- Nix can now `warn` when an unkwown experimental feature is passed
(making it much nicer to spot typos and spot deprecated features)
- It’s now easy to remove a feature altogether (once the feature isn’t
experimental anymore or is dropped) by just removing the field for the
enum and letting the compiler point us to all the now invalid usages
of it.
The boolean is only used to determine if the formals are set to a
non-null pointer in all our cases. We can get rid of that allocation and
instead just compare the pointer value with NULL. Saving up to
sizeof(bool) + platform specific alignment per ExprLambda instace.
Probably not a lot of memory but perhaps a few kilobyte with nixpkgs?
This also gets rid of a potential issue with dereferencing formals based on
the value of the boolean that didn't have to be aligned with the formals
pointer but was in all our cases.
I found it somewhat confusing to have an error like
error: attribute 'getFlake' missing
if the required experimental-feature (`flakes`) is not enabled. Instead,
I'd expect Nix to throw an error just like it's the case when using e.g. `nix
flake` without `flakes` being enabled.
With this change, the error looks like this:
$ nix-instantiate -E 'builtins.getFlake "nixpkgs"'
error: Cannot call 'builtins.getFlake' because experimental Nix feature 'flakes' is disabled. You can enable it via '--extra-experimental-features flakes'.
at «string»:1:1:
1| builtins.getFlake "nixpkgs"
| ^
I didn't use `settings.requireExperimentalFeature` here on purpose
because this doesn't contain a position. Also, it doesn't seem as if we
need to catch the error and check for the missing feature here since
this already happens at evaluation time.
Without this, flakes within the same tree and same lock data will have
the same fingerprint and the eval cache for one flake will be
incorrectly used for another.
Maximilian Bosch
Yorick